1. The Field of the Invention
The present invention relates generally to apparatus for deceleration of projectiles, and containment of those projectiles and their fragments and particulates resulting therefrom. More particularly, it concerns apparatus in which an impacting projectile is fragmented, its forward momentum mostly stopped but partially reflected into a generally predictable splatter zone which is then confined by successive impact plates in a partially or completely contained cavity. The bullets, fragments and resulting particulate matter are then collected and confined for disposal or recycling.
2. The Background Art and Background of the Invention
It is understood that when a projectile such as a bullet strikes an object, the original energy of the projectile, which is conserved, will be transformed into one or more of several other forms including: deformation of the projectile, deformation of the object, reflected motion of the projectile, and reflected motion of the object.
When the object of sufficient inertia to retain its original momentum after the impact of a bullet, and the object is composed of a material possessing sufficient strength and other resiliency to resist significant deformation from the impact, an analysis of the impact may reasonably be restricted to the effects upon the bullet, including both deformation and reflected motion.
The term "reflected motion" is used broadly herein and refers to the new, changed momentum vector of a projectile which is a result of an impact with an object. The terms "bullet" and "projectile" are used broadly and interchangeably herein. They refer to the original body as placed in motion, as well as any fragments or particulate matter formed as a result of impacts with another object.
When the object being struck is a planar surface (a plate) and meets the high-inertia, high-strength criteria described above, the resultant reflected motion can be readily described in terms of two characteristics: exit zone, and bullet integrity. These quantities are generally related to several variables, among which some of the most significant are bullet composition, angle of incidence, and bullet velocity. Assuming a relatively constant range of both bullet compositions and bullet velocities, a relevant analysis can be derived from the angle of incidence alone.
When a bullet strikes a plate at an extremely low angle, close to 0 degrees, the bullet integrity remains essentially intact. The exit zone is also changed very little from the angle of incidence, generally running generally parallel to the surface of the plate.
As the angle of incidence is increased, the most notable effect is that the bullet begins to lose a small part of its integrity as it exits the point of impact. Because the projectile can no longer be characterized as a point, it is most helpful to analyze the now multiple exit trajectories as a zone. At relatively low angles, approximately from 0 to 25 degrees most of the fragmented matter from the bullet continues to travel in roughly the same direction as the main body of the bullet. However as the angle is continually increased, the zone begins to more closely resemble a fan shape, emanating radially from the point of impact in something generally less than a 180 degree spread.
An additional result of increasing the angle of incidence is that the exit angle, in relationship to the surface of the plate begins to increase slightly as well. It is generally not complementary to the angle of incidence as it would be in an analysis of a more elastic media. Rather, the exit angle tends to range from 0 to 20 degrees as some function of the angle of incidence, which ranges from 0 to 90 degrees.
As the angle of incidence is increased above 45 degrees, another effect begins to become evident. The fan shape of the exit zone begins to spread to angles generally greater than 180 degrees, the effect of which is that, given sufficient angle of impact, the zone begins to resemble a cone whose pinnacle is at the point of impact and whose sides extend outward from that point at the exit angle (see FIG. 4).
As the angle of incidence begins to approach 90 degrees, this effect, in combination with the increasingly complete destruction of the bullet integrity at high impact angles produces an exit zone which is almost entirely composed of extremely low-mass fragments, and forms a uniform, relatively predictable cone shape.
Target practice is an activity pursued by many to enhance shooting skills, as criteria of employment, or for sport. It is customary in target practice to provide a means of stopping projectiles after they have traveled through or by a target, and before their potential to harm persons or damage property is concluded. This is traditionally accomplished by such means as providing adequate proximity between the target and persons and property or by constructing a barrier such as an earthen berm or a wall to stop the path of the projectile. In light of modern weapons with long and powerful trajectories, proximity solutions involve massive amounts of valuable land resources and are therefore often unfeasible in all but the most remote areas.
Merely providing an earthen or other barrier may stop the bulk of the projectiles, but has no effect on the indiscriminate distribution of lead, the primary material used for bullets, into the environment. Lead is a heavy metal environmental contaminant increasingly implicated as a health risk to humans and animals.
Simple barriers may stop a projectile, but allow lead fragments or particulates to escape into the environment. Barriers without containment deflect bullets which may retain enough energy to harm bystanders, shooters, or property. Thus, these solutions still require a significant, additional proximity solution.
The term "plate" is used herein in its broadest sense as a planar sheet of material capable of stopping or deflecting a projectile and its fragments. It will be understood by those of ordinary skill in the art, that selection of plate material is made in consideration of the nature and velocity of the various projectiles to be stopped and contained. For most firearms, the material of choice may be hardened steel plate or the equivalent. Furthermore, plates intended to take primary, direct impacts will necessarily be stronger than those intended to take secondary or tertiary impacts.
For purposes of technical description, the terms "front," "back," "side, " "top" "bottom," etc shall be used as they relate to the perspective of a shooter firing a projectile into the bullet trap.
Recent emphasis has been placed on stopping and containing projectiles by the use of bullet traps and stops, and containment systems employing a variety of configurations intended to stop a projectile and contain the resultant products. For example, in U.S. Pat. No. 4,821,620, to Cartee et al. (1989), it is described to provide a screen of rubber-like material followed by a deflector plate. The bullet is said to travel through the screen and be diverted by the plate down toward the collector bin at the base of the device. The close proximity of the rubber-like material to the plate, combined with the angle at which the plate is disposed, produce the particular disadvantage of exposing the rubber-like material to relatively high-energy reflections of the bullet off the plate, therefore causing the material to quickly wear out and/or to allow bullets to escape back through the screen with enough energy to cause harm to persons or property.
Others including Baravaglio in U.S. Pat. No. 4,512,585 (1985), and Pencyla in U.S. Pat. No. 3,737,165 (1973), and Nikoden in U.S. Pat. No. 2,772,092 (1954), describe systems consisting of a collection of impact plates oriented at angles to the trajectory of the bullet which direct the bullet, relatively intact, backward or downward into an area where it is decelerated in some sort of generally rounded chamber. The curved plates, the number of plates and the need for a variety of other fabricated components make these devices generally expensive to manufacture, assemble, and service. Additionally, these devices generally suffer the disadvantage that bullet accumulations in the collection bins are not easily accessible to the user to facilitate removal of the lead.
Others including Wagoner in U.S. Pat. No. 4,126,311 (1978), and Coburn in U.S. Pat. No. 5,070,763 (1991), and this inventor, Bateman, in my co-pending U.S. patent application Ser. No. 08/204/682, have more effectively dealt with the problem of lead removal by describing long, generally funnel-shaped openings which direct projectiles through a relatively small aperture where they enter a containment chamber and are decelerated by one method or another. All these and similar devices require large quantities of plate material in order to form the relatively low angles required to guide the bullet into the chamber without destroying its integrity. The depth of such traps often must range from 15' to 40' in order to obtain a typically required vertical front opening of 8' to 10'. The cost of the plate required creates an obvious disadvantage to suppliers competing to produce such apparatus. Furthermore, the amount of space required for the bullet trap is a disadvantage in instances where the cost of land or surrounding facilities should be minimized or in instances where an existing shooting range only has a limited amount of space in which to place the trap.
Another problem yet unsolved by the prior art is containment of fine fragments and particulate matter created on impact without the problems associated with "deep" bullet traps or other complex or expensive arrangements. For example, Wojcinski in U.S. Pat. No. 5,171,020 (1992), describes a device consisting of a back plate and an elastic facing which form a containment chamber which is then filled with a mass of granulated rubber material. In theory, as the bullet passes through the granulated material, its velocity is slowed completely, or significantly enough that any impact with the back plate will not cause damage to the plate or the projectile. While this device appears to solve the containment problem, it can only do so at great cost. Specifically, the volume of granulated material needed in practice tends to be unmanageable. And once the elastic facing becomes destroyed, it must be replaced or repaired. In order to perform this maintenance, all the granulated material must be removed, stored, and then replaced which procedure can be time consuming, expensive, and potentially even dangerous.
W. German Patent 31-31-228 describes a similar device which, rather than granulated rubber, uses rubber-like sheets called "lamellas" hung from above in a pattern parallel to one another, all at an angle to the trajectory of the bullet. As the bullet penetrates the layers of lamellas, eventually its velocity is slowed or stopped. Spent bullets are intended to drop down between the lamellas and to the floor where they can be collected. While this device solves several of the stated problems, in practice, the lamellas soon become worn in the areas of highest bullet concentration. Because the lamellas form the primary deceleration mechanism, in their worn state, they may allow bullets to pass completely through the trap causing an extremely dangerous hazard to persons or property behind the trap.
In short, all known prior art employs a variation of one of two fundamental deceleration methods: 1) to use plates oriented at relatively low angles to the trajectory of the bullet and thereby direct the bullet, somewhat intact, into successively more controllable trajectories; or 2) to use a permeable material which gradually decelerates the projectile, but suffers its own partial destruction in the process.
Those having ordinary skill in the art will appreciate that the present invention is therefore unique and also meets the outlined needs as well as needs not specified herein.